Preservation system for volatile memory with nonvolatile backup memory

Abstract

In a preservation system for a volatile memory associated with a nonvolatile memory, an energy storage portion accumulates energy while power is provided normally. When a power outage occurs, the stored energy is supplied to the volatile memory. Enough backup power is stored to accommodate the vast majority of unintentional interruptions of power. Eventually, after removal of external power, when the backup power decreases to a predetermined amount, data in the volatile memory is transferred to the nonvolatile memory. The preferred use for the preservation system is in an environment with vibration and/or power switching transients that affect the supply of power, such as an aircraft.

What is claimed is: 
     
       1. An apparatus for providing memory power, comprising: means for receiving external power;   volatile memory means for storing data while at least a first level of power is provided;   nonvolatile memory means for storing data;   backup power storage means for storing said external power and for providing backup power to said volatile memory means at a level higher than said first level during an outage of said external power; and   control means for transferring data from said volatile memory means to said non-volatile memory means in response to the detection of an outage of said external power, and for delaying said transfer until said backup power falls below said first level of power.   
     
     
       2. The apparatus of claim 1, in which said transfer is delayed for a predetermined time sufficient to prevent said transfer of data in a substantial portion of temporary outages of said external power. 
     
     
       3. The apparatus of claim 1, wherein said nonvolatile memory means comprises at least one semiconductor EEPROM. 
     
     
       4. The apparatus of claim 1, wherein said backup power storage means includes a plurality of capacitors connected to be charged from the supply of said external Dower. 
     
     
       5. The apparatus of claim 2, in which said transfer is delayed for a predetermined time sufficient to prevent said transfer in a majority of said temporary outages. 
     
     
       6. The apparatus of claim 1, in which said means for receiving external power is adapted to receive power from an aircraft power supply system. 
     
     
       7. The apparatus of claim 1, in which said volatile and non-volatile memory means are solid-state. 
     
     
       8. An apparatus for providing memory power, comprising: means for receiving external power;   volatile memory means for storing data while a first level of power is provided;   nonvolatile memory means for storing data while power is not provided;   backup power storage means for storing said external power and for providing the stored external power as backup power to said volatile memory means during an outage of said external power: and   control means for controlling transfer of the data stored in said volatile memory means from said volatile memory means to said nonvolatile memory means when said backup power falls below said first level of power and for providing a count of a number of transfers of data from said volatile memory means to said nonvolatile memory means.   
     
     
       9. The apparatus of claim 1, wherein said control means is operative, upon start-up, to prevent said transfer from said volatile memory means to said nonvolatile memory means until said backup power rises to a second level of power. 
     
     
       10. A preservation system for volatile memory means used in an aircraft to store data while a first level of external power is provided, comprising: nonvolatile memory means for storing data while power is not provided;   backup power storage means for storing said external power and for providing the stored external power as backup power to said volatile memory means during an outage of said external power; and   control means for controlling transfer of the data stored in said volatile memory means from said volatile memory means to said nonvolatile memory means when said backup power falls below said first level of power and for providing a count of a number of transfers of data from said volatile memory means to said nonvolatile memory means.   
     
     
       11. An apparatus for providing memory power, said apparatus comprising, in combination, a volatile memory in which data can be stored and from which data can be retrieved by a computer except when data is stored in, or is being transferred to or from a non-volatile memory for data preservation,   a non-volatile memory for storing data transferred from said volatile memory,   means for conducting power from an external power source to said volatile memory,   a backup power supply for supplying power to said volatile memory during power outages of said external source, and   a data transfer control device for detecting said power outages and supplying backup power to said volatile memory and preventing data transfer from said volatile memory to said non-volatile memory during each of said power outages for a predetermined length of time, said length of time being sufficient to prevent said data transfer for a substantial portion of temporary outages of said external source, and for causing said data transfer to occur after an outage has persisted longer than said predetermined length of time.   
     
     
       12. Apparatus as in claim 11 in which said backup power supply includes a power storage device for storing power from said external source and delivering its stored power upon detection of one of said outages. 
     
     
       13. Apparatus as in claim 11 in which said apparatus is provided in or for an aircraft computer system. 
     
     
       14. Apparatus as in claim 11 in which said substantial portion is a majority of said temporary outages. 
     
     
       15. An apparatus for providing memory power, said apparatus comprising, in combination, a volatile memory for storing data,   a non-volatile memory for storing data transferred from said volatile memory,   said non-volatile memory being capable of executing a limited number of read-write cycles before it wears out,   means for conducting power from an external power source to said volatile memory,   a backup power supply for supplying power to said volatile memory during power outages of said external source, and   a data transfer control device for detecting said power outages and supplying backup power to said volatile memory and preventing data transfer from said volatile memory to said non-volatile memory during each of said power outages for a predetermined length of time, said length of time being sufficient to prevent said data transfer for a substantial number of temporary outages of said external source, and for causing said data transfer to occur after an outage has persisted longer than said predetermined length of time,   whereby said number of read-write cycles for a given length of operating time for said memory is substantially limited.   
     
     
       16. Apparatus as in claim 15 in which said apparatus is provided in or for an aircraft computer system, and said external power source is an aircraft power supply system. 
     
     
       17. A method of controlling data storage and retrieval in an aircraft computer system having a volatile memory and a power supply, said power supply being subject to relatively frequent temporary power outages, said method comprising the steps of: (a) determining the duration of the majority of said temporary power outages;   (b) providing backup power from a backup power supply;   (c) providing a non-volatile memory for storing data transferred from said volatile memory to prevent data loss;   (d) detecting the onset of each of said temporary power outages;   (e) supplying back-up power to said volatile memory during each of said outages; and   (f) during each outage, transferring data from said volatile memory to said non-volatile memory only after the duration of said outage becomes greater than the duration of a majority of said temporary outages.   
     
     
       18. A method as in claim 17 in which said nonvolatile memory is limited in the total number of read-write cycles it is able to execute. 
     
     
       19. A method as in claim 17 in which said backup power is developed by charging a charge storage device from said power supply and releasing that stored charge upon detection of an outage. 
     
     
       20. A method as in claim 17 in which said computer system is disabled when data is transferred out of said volatile memory memories. 
     
     
       21. A method as in claim 18 including the step of counting said cycles to give information regarding the remaining life of said non-volatile memory. 
     
     
       22. A method of limiting the computer down time and data transfer operations in a computer system having a power supply, a volatile memory for use in the operations of said computer system, and a non-volatile memory for storing data from the memory to protect it from destruction due to temporary power outages, said method comprising the steps of: (a) detecting the onset of each of said outages and supplying backup power to said volatile memory in response thereto;   (b) maintaining said backup power during each outage for a predetermined time longer than the duration of a majority of said power outages; and   (c) transferring data from said volatile memory to said non-volatile memory only if said outage lasts longer than said predetermined time.